The subject matter disclosed herein relates generally to electrical equipment and, more particularly, to signal injection systems that facilitate monitoring of electrical equipment while the equipment is in service.
Many known pieces of electrical equipment are placed in service for extended periods of time. Such known electrical equipment includes motors, generators, transformers, and power cables. These extended operational periods may last for weeks and months and removing such equipment from on-line service merely to perform preventative maintenance checks may be impractical. However, regardless of the operating condition of the electrical equipment, routine preventative maintenance and operational checks of portions of the equipment need to be performed. Such preventative maintenance and operational checks include measuring values of monitored components such as a resistance provided by insulating materials associated with the electrical devices, for example, insulation between motor/generator/transformer windings and proximate components at ground potential.
At least some known extended-use electrical equipment includes monitoring systems that transmit high-frequency and low-voltage signals into the on-line electrical equipment to measure the properties of the monitored components. However, due to the low impedance of the power transmission portion of the electrical equipment, and the high impedance of the monitored components, a significant portion of the signals is transmitted through the power transmission portions and only a small fraction of the signals are transmitted to the monitored components. Therefore, the low signal strength transmitted to the monitored components increases the ambiguity of the measured values and, therefore, reduces the reliability of those values. Adding high-inductance components in direct contact with the power transmission portions is expensive in that the additional components need to be rated for extended exposure to the line currents of the equipment. Moreover, at least some known electrical equipment does not have a component configuration that defines sufficient unused space for such high-inductance components.